In a Class-AB output stage, a crossover distortion is proportional to a ratio between an output current and a quiescent current. Therefore, there is a trade-off between the crossover distortion and the quiescent current. Specifically, in order to always lower the crossover distortion not matter if the output current is large or small, the quiescent current may be designed larger to improve the performance, but the larger quiescent current means large power consumption.
To solve this problem, one solution is using two different output stages in the amplifier circuit. For example, when an input signal has a lower strength (i.e. lower output current of the amplifier circuit), the amplifier circuit may select one of the output stages to generate an output signal, and when it is detected that the input signal becomes large (i.e. larger output current of the amplifier circuit), the amplifier circuit may select the other output stage to generate the output signal. However, designing two output stages may need more chip areas, and the switching operation between the two output stages may cause a glitch of the output signal.